In many telephone systems, the telephony terminals provide the option of dialing the desired subscriber by using the direct dialing keys. For this purpose the dialing keypad offers a series of keys that can be configured for connection to a specific subscriber. Sometimes dialing such a direct dialing function within a private telephone system shows whether the connection is busy at the desired subscriber. In addition, in such private systems an LED next to each direct dialing key can continuously signal information about the busy state of the associated subscriber.
In practice, a single direct dialing key is usually not sufficient for each subscriber because almost every subscriber can be reached via a number of connections, for example, at the office, private or mobile. Therefore, in a conventional solution, a number of direct dialing keys are assigned to one single subscriber. As a result both the clarity on the keypad is reduced and it is not possible to make optimum use of the existing keys for as many subscribers as possible. Therefore, by using an toggle key, at least two possible call numbers are assigned to one single key. However, even in the above mentioned simple example of connections at the office, private or mobile, the two dialing options provided by toggling are insufficient.
Therefore, actuating the direct dialing key frequently does not make a connection to the desired subscriber because the line is busy or the dialed subscriber is unavailable under the selected number. In the case of conventional methods, the busy state can then at most be read at the LED provided the subscriber's line is in the same private telephone system. Therefore, this functionality is restricted to the limited circle of possible subscribers and cannot be used beyond the boundaries of the private telephone system.
In addition, availability of the subscriber cannot be interrogated via direct dialing keys in conventional telephone systems and the busy state the user does not provide the user with any information about the availability of the desired subscriber. At least one availability service is indeed frequently provided within a company. However, it is not accessible via the telephone system. This means that important additional information about the availability of the subscriber such as “in a meeting”, “on holiday”, “represented by . . . ” cannot be accessed with the direct dialing key.